Preterm infants exhibit growth patterns that place them at high-risk for growth faltering. What is not clear are the mechanisms that contribute to growth faltering in preterm infants. Only by understanding the process of growth in preterm infants can nursing strategies be developed to prevent growth faltering. The purpose of this study is to develop a theoretical model that explains growth faltering. Behavioral and physiologic characteristics of the preterm infant may play a role. The specific aims of this study are to examine change over time in selected infant behavioral variables (interactive and feeding behaviors) and physiologic variables (growth velocity, nutritional intake, sleep patterns, heart rate variability, biologic status, and birthweight) and the relationship of these variables to growth patterns. Longitudinal data will be collected at one, two, four, six, and eight months post- term age. Inclusion criteria will include gestational age less than or equal to 35 weeks, appropriate for gestational age, and normal physical and neurodevelopmental exam at discharge. For all data points the following data will be collected: observation of interactive behavior; observation of feeding behavior; growth velocity expressed by grams of weight gain per day; nutritional intake as assessed by calories/kg/day and protein/ kg/day; sleep patterns as assessed by amount of time spent in quiet sleep, active sleep, and awake; heart rate variability as assessed by standard deviation and spectral analysis; and biologic status will be the severity of the initial hospital course and health status post-discharge. Findings from this study may provide evidence for a model of explain growth faltering.